Vertically-opening goods-handling doors are commonly provided on industrial premises and warehouses for opening and closing several times a day. In most cases, it is important to reduce heat exchange between the inside and the outside, and rapid-acting systems are therefore provided. In practice, such systems can only be provided for relatively light curtain doors, i.e. doors which do not require large actuation forces. Thus, present doors of this type, regardless of whether they are doors of the concertina type or doors of the type wound onto a shaft (which shaft may be placed at the top or bottom of the curtain), comprise a flexible curtain which may optionally be stiffened at regular intervals by reinforcing bars. In the following description, a concertina-type door is used as an example for describing the invention, however it must naturally be understood that the invention is applicable to any vertically-opening door performing a similar function.
In a particular prior art embodiment of a concertina-type door, there are:
two channel-section metal risers having their top ends interconnected by a beam which supports drive means essentially constituted by a motor and a shaft for winding up door-raising straps; PA1 a flexible curtain which is stiffened at regular intervals by horizontal reinforcing bars; and PA1 lifting straps which are fixed at one end to the bottom reinforcing bar of the flexible curtain and at the other end to the shaft onto which they are wound when the shaft is driven by the motor.
Preferably, the lifting straps pass through guides disposed on at least some of the reinforcing bars. Some of the reinforcing bars, including the bottom bar, have guide wheels disposed at each end for guiding the sides of the curtain along the channel-section risers while protecting said edges from wear which would arise from their coming directly into contact with said risers.
In order to prevent drafts flowing round the sides of the flexible curtain as guided by the risers, various solutions have been suggested in the past. One of these solutions is described in Nergeco's French patent application number 85/02826 and consists in providing the concertina-type door with moving sealing members fixed to the sides of the flexible curtain. In said patent application, the flexible curtain includes respective strips of flexible material mounted on each of its side edges and pressing against the webs of channel-section risers, said strips extending beyond the longitudinal extent of the guide wheels. Such strips may be made of rubber including optional transverse notches, or else by a stack of at least two such notched strips with the notches being offset relative to each other, or else by a brush having long and flexible bristles, or by the side edges of the curtain itself, which edges are made too long specifically for this purpose, or finally by any other flexible material in any suitable form for providing the same draft-excluding function.
The draft-excluding strips described in the above-mentioned patent application are highly effective, however they are vulnerable in two different ways. Firstly by sliding in direct contact with the channel-section risers which are generally made of fairly rough metal, they suffer rather rapid wear. Secondly, when fitted to doors that are exposed to fairly intense cold on one of their faces, they frequently become stuck to the metal risers by frost. When a concertina-type door fitted with side draft-excluding strips such as those described above is used for separating two volumes having ambient temperatures respectively above and below 0.degree. C., for example a door to a deep-freeze warehouse opening to the outside, or opening to premises where the ambient temperature is greater than 0.degree. C., it has been observed that ice forms in the risers between the draft-excluding strips and said risers. The ice jams the reinforcing bars of the curtain together with the guide wheels fixed thereto and sticks the draft-excluding strips to the risers, thereby preventing the curtain from operating. This prevents the concertina-type door from opening or closing. This is due to water vapor migrating between the two spaces, and in particular to water vapor entering the space at less than 0.degree. C. from the space where the ambient temperature is greater than 0.degree. C. As a result the water vapor condenses on the risers and on the draft-excluding strips and is then transformed into ice on those portions thereof which are at a temperature below freezing.
Preferred embodiments of the present invention mitigate these drawbacks.